A conventional synchronous motor typically uses rotor position sensors to provide information regarding the position of the motor's rotor with respect to the motor's stator windings. Rotor position sensors such as Hall effect devices are typically mounted in the stator, proximate the stator windings. The rotor position sensors provide rotor position information, which allows for proper control for the conversion of power that is supplied to the stator windings of an electrical machine.
However, rotor position sensors can be unreliable due to mechanical alignment problems (e.g., problems caused by bearings) and temperature incompatibility problems between the stator windings and electronic components such as the Hall effect devices. Moreover, the rotor position sensors can be difficult to mount to the motor during motor assembly, especially for multi-pole motors. In multi-pole motors, the electrical misalignment angle is equivalent to the angular mechanical misalignment angle multiplied by the number of pairs of poles.
In response to the problems with rotor sensors, position sensorless control techniques have been developed for controlling the speed of the synchronous machines.
U.S. Pat. No. 6,301,136 to Huggett et al., which is incorporated herein in its entirety, discloses a floating synchronous reference frame controller, which advantageously provides a floating synchronous reference frame for controlling an inverter to drive a synchronous motor. However, due to the coupling impact of the motor circuitry in floating synchronous reference frame (as will be described later) delays exist during transients during which the estimated angle of the current Park vector differs from the actual angle of the current Park vector. Also, the coupling impact of the motor equivalent circuit in floating synchronous reference frame forces the gain of the regulator used for angle estimation to be kept small which slows down the system response. A further result of using a small gain is a significant delay in reducing the error between the estimated angle of the current Park vector and the actual angle of the current Park vector during slow transients, such as acceleration and deceleration, as well as fast transients, such as step changes. Because undesirable imaginary axis current flows in the machine during these delays, longer delays may require substantial overrating of the inverter and electrical machine.
Ideally, only real-axis current flows in the machine, as the floating synchronous reference frame is by definition aligned with the real axis component of the current Park vector.
Thus, there is a need for faster, more robust, more accurate sensorless estimation of the angle of the current Park vector that minimizes imaginary axis component of the current Park vector, and avoids the need for overrating of inverters and PM machines.